Bacteria agglutinating glycoprotein (BAGP) from saliva is isolated from unstimulated parotid saliva collected from one donor. The isolation procedure includes 5 steps, one being affinity absorption to the strain in a batch system. The conditions for desorption have to be carefully controlled. The resulting glycoprotein fraction is pure as judged from SDS electrophoresis in a polyacrylamide gradient under reducing conditions and by immunoelectrophoresis. Hybridoma antibodies obtained after fusion of spleen lymphocytes from NIH general purpose mice (N:GP(S)) and of SP2 mice myeloma cells, inhibit the agglutinating activity of the BAGP in the assay system. The monoclonal antibody is presently isolated from the tissue culture supernatant and from ascites fluid from nude mice injected intraperitoneally with hybridoma cells.